1. Field of the Invention
This invention relates to a resistor excellent in micro-linearity characteristic and in wear resistance and a variable resistor that uses the resistor.
2. Description of the Related Art
A conventional resistor used for a variable resistor of various sensors contains resin serving as based material of the resistor, carbon fiber serving as structural material, and carbon black serving as conducting particle, and a slider moves in contact with a resistor pattern consisting of the resistor. At that time, because hard carbon fiber receives the load of the slider in the diametral direction and distributes the load along the long carbon fiber, the load wears the resistor very little. Therefore, the wear resistance of the variable resistor that uses this type of resistor is excellent in comparison with the variable resistor that uses another type of resistor that contains only conducting particles such as carbon black or graphite.
However, in the case of a conventional resistor that uses carbon fiber, because carbon fiber has high conductivity in the fiber direction, the resistivity varies in a small range of the resistor depending on the fiber orientation of carbon fiber, and the micro-linearity characteristic is poor, and the poor micro-linearity is a problem.
The micro-linearity characteristic is described herein under. FIG. 14 shows a graph obtained in a test. In the test, a rating voltage V.sub.in is applied in the length L direction of a resistor pattern, and the vertical axis represents the output V of a slider that slides on the resistor pattern in the longitudinal direction and the horizontal axis represents the position X of the slider on the resistor pattern. The output change concomitant with displacement .DELTA.X of the slider from an arbitrary point on the resistor is represented by an ideal straight line P having a gradient V.sub.in /L on the assumption that the resistivity of the resistor is constant not depending on the position.
On the ideal straight line P, the normal output voltage obtained when the slider moves from A point to B point by .DELTA.X is represented by .DELTA.V=(.DELTA.X/L).times.V.sub.in, but the actual output S deviates from the ideal straight line P. As shown in the equation (1), the micro-linearity characteristic is calculated as described herein under. The normal output variation is subtracted from the output variation V.sub.A -V.sub.B (V.sub.A is the actual output at the point A and V.sub.B is the actual output at the point B) to obtain the difference, the difference is divided by the applied voltage, and the obtained value is multiplied by 100 to obtain percent expression. In the case of high performance position sensor, particularly excellent micro-linearity characteristic, which shows actual output S is similar to the ideal straight line P, is required.
[Equation 1]
micro-linearity ##EQU1##
V.sub.A : output value obtained when the slider is positioned at the point A PA0 V.sub.B : output value obtained when the slider is positioned at the point B PA0 V.sub.in : applied voltage in the resistor length L direction PA0 .DELTA.X: distance between the point A and the point B PA0 L: resistor length